Transdermal methods have been devised for administering controlled quantities of systemically active drugs. However, to be useful, the drug must be permeable through the skin. Even if permeable, the method may still not be useful because of irritation caused to the skin. This is especially important with certain drugs in which the continuous supplying of a therapeutic drug over an extended period of time is highly desirable. Unfortunately, some drugs such as timolol while adaptable to therapy via a transdermal system by virtue of being absorbable through the skin, heretofore have not been adaptable to long term therapy because of the irritation caused to the skin. By "extended period" as herein employed is meant time which is long enough to be measured in numbers of days.